Aluminum alloy



Patented Feb. 9, 1926.

UNITED STATES PATENT OFFICE.

RODERICK L. JOHNSTON, OF PLAINFIELD, NEW JERSEY, ROBERT S. ARCHER, OFLAKE- :WOOD, AND ZAY JEFFRIES, OF SHAKER HEIGHTS, OHIO, ASSIGNORS TOALUMINUM COMPANY OF AMERICA, 0]? PITTSBURGH, PENNSYLVANIA, A CORPORATIONOF.

PENNSYLVANIA.

ALUMINUM ALLOY.

No Drawing- 0rigina1 application filed November 27, 1920, Serial No.426,793. Divided and this application filed February 11, 1925. SerialNo. 8,517.

To all whom it may concern:

Be it known that we, RODERICK L. J OHNS- TON, of Plainfield, county ofUnion, and State of New Jersey, ROBERT S. ARCHER, of Lakewood, and ZAY JEFFRIES, of Shaker Heights, both in the county of Cuyahoga and State ofOhio, all citizens of the United States of America, have inventedcertain new and useful Improvements in Aluminum Alloys, of which thefollowing is a full, clear, and exact description.

The presence of small amounts of silicon in aluminum and in aluminumalloys is usually considered objectionable. In the course of aninvestigation upon the effects of silicon we have discovered that byusing a substantial amount of silicon, materially greater than thequantity usually found as an impurity, with the addition of a metal ormetals, for example one or more of those hereinafter named, it ispossible to produce an alloy having excellent casting qualities combinedwith good physical properties.

Among the metals capable of forming solid solutions in the aluminum wehave found copper and zinc particularly advantageous. The metalsreferred to may be used singly or in combination. In the use of copperalone, the silicon content of the alloy should in general be not lessthan about 3 percent nor more than about 10 per cent, and the coppershould be preferably from about 2 per cent to about 5 per cent; theproportions of copper and silicon being variable, however, according tothe particular combination of properties desired. In general, theattainment of good casting qualities depends largely upon the relativeproportions of the silicon and copper, the latter being preferablyreduced as the former is increased, and vice versa. Increasing thecopper, at least up to the limit of its capacity for entering into solidsolution in the aluminum, tends in general to increase the tensilestrength, especially if subjected to a suitable heat treatment, say thatdescribed in Patent No. 1,508,556, issued September 16, 1924, to ZayJeflries and Robert S. Archer. A test bar cast in sand in the ordinaryway, of an aluminum alloy containing 10 per cent silicon and 3 per centcopper, showed a tensile strength of about 23,000 pounds per square inchand an elongation of about 1.5 per cent in two inches. Such a bar, afterheat treatment by the method described in the above mentioned patent,showed an increase of tensile strength up to 30,000 pounds per squareinch and an increase of elongation up to 2.5 per cent. A bar of the samealloy but cast in a chill mold, in order to cause rapid solidificationof the molten metal, was found to have a tensile strength of about30,000 pounds per square inch and an elongation of about 2.7 per cent,even without heat treatment. A similar bar, heat treated, had a tensilestrength of 40,000 pounds per square inch and 6 per cent elongation. Onthe other hand, a chill-cast heat-treated bar of an alloy containingabout 6 per cent silicon and about 4: per cent copper was found to havea tensile strength exceeding 42,000 pounds per square inch and anelongat-ion exceeding 8 per cent in 2 inches. Alloys of aluminum,silicon and copper are described and claimed in our copendingapplication identified hereinafter.

The addition of zinc up to about 5 per cent has a slight effect on thetensile strength of the alloy. Above that amount a greater increase oftensile strength is observed. The presence of the zinc is often anadvantage by reason of the whiter color of the polished alloy. We havefound that with the addition of an alkali metal or metals to the alloy,as described in patent of Junius D. Edwards, Francis C. Frary and HarryV. Churchill, No. 1,410,461, issued March 21, 1922, very satisfactoryphysical properties can be obtained along with the other advantagesincident to the presence of the zinc, particularly if the alloy to whichalkali metal has been added is cast in such a manner, as for example bythe use of a chill mold, that the molten metal is caused to solidifyrapidly. For instance, an alloy containing about 10 per cent zinc andabout 8 per cent silicon, to which alkali metal had been added and whichwas cast in a chill mold, has been found to have a tensile strengthexceeding 42,000 pounds per square inch, with an elongation up to 7 percent in two inches. A similar casting, after being subjected to and anelongation of 1.5 per cent.

the heat treatment described in the above mentioned patent of Archer andJefiries, showed a decrease of tensile strength to about 35,000 poundsper square inch, but an increase of elongation up to 14 per cent.

In the case of aluminum-silicon alloys containing both copper and zinc,a sand cast test bar of an alloy containing 8 per cent silicon, 10 percent zinc and 2.5 per cent copper, was found to have a tensile strengthof 27,000 pounds per square inch This alloy is also susceptible toimprovement by addition of alkali metal before casting; sand castspecimens of the alloy'so treated having a tensile strength of 30,000pounds per square inch with an elongation of 2 per cent, while chillcast specimens have a tensile strength of 38,000 pounds per square inchand an elongation of 3.5 per cent. Heat treatment by the methoddescribed in the patent of Archer and Jefiries before referred to hasbeen found to increase the tensile strength of the chill cast alloy upto 45,000 pounds per square inch and at the same time increase theelongation to 7.5 per cent.

In the alloys referred to above we have observed that the elongation isbetter if the iron content is low, and for that reason there are manycases where the iron should not exceed about 0.6 per cent. In othercases much higher iron can be used, especially in chill castings, as forexample pressure die castings.

The alloys described herein are also well adapted to forging and likeoperations.

While in certain of the claims certain percentages and limits have beenstated it is to be understood that they may be somewhat departed fromwithout departing from the invention sought to be protected, so long asthe properties of the alloy are retained.

This application is a division of our copending application, Serial No.426,793, filed November 27, 1920.

We claim:

1. An alloy composed chiefly of aluminum, containing, approximately,silicon 8 per cent, zinc 1.0 per cent, and copper 2.5 per cent.

2. An alloy. composed chie fly of aluminum, containing silicon between 3and 10 per cent, and zinc, the latter not exceeding about 15 per cent.

3. An alloy composed chiefly of aluminum, containing silicon between 3and 10 per cent, and zinc between 5 and 15 per cent, approximately.

4. An alloy composed chiefly of aluminum, containing about 8 per centsilicon, an:l about 10 per cent zinc.

5. An alloy composed chiefly of aluminum, containing, approximately,silicon 8 per cent, zinc 10 per cent, and copper 2.5 per cent, with aniron content not exceed ing about 0.6 per cent.

6. An alloy composed chiefly of aluminum, containing silicon between 3and 10 per cent and zinc, the latter not exceeding about 15 per cent,with an iron content not exceeding about 0.0 per cent.

7. An alloy composed chiefly of aluminum, containing about 8 per centsilicon and about 10 per cent zinc, with an iron content not exceedingabout 0.0 per cent.

In testimony whereof we hereto afiix our signatures.

RODERICK L. JOHNSTON. ROBERTS. ARCHER. ZAY JEFFRIES.

